THE XMASS EXPERIMENT MAR. 8 TH , 2019 Y. KISHIMOTO ON BEHALF OF XMASS COLLABORATION KAMIOKA OBS., ICRR, THE UNIV. OF TOKYO KAVLI IPMU, THE UNIV. OF TOKYO
CONTENTS • XMASS project • Physics results from XMASS • Low background technique in XMASS • Summary
THE XMASS PROJECT XMASS: a multi purpose experiment with liquid xenon Dark matter Solar neutrino (pp/7Be) 0ν ββ KamLAND Located 1,000 m underground (2,700 m.w.e.) at the Kamioka Observatory in Japan Super-Kamiokande CANDLES Features E-GADS Scalability XMASS Low energy threshold (~0.5keVee) Sensitive to e/ g events as well as nuclear recoil CLIO NEWAGE 3
XMASS-I DETECTOR Liquid xenon detector 832 kg of liquid xenon (-100 o C) 642 2-inch PMTs (Photocathode coverage >62%) Each PMT signal is recorded by 10-bit 1GS/s waveform digitizers 80cm Water Cherenkov detector 11m 10m diameter, 11m high 72 20-inch PMTs Active shield for cosmic-ray muons Passive shield for n / g 4 10m
HISTORY OF XMASS-I DATA-TAKING 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 Run end on Dec. May Nov. Feb. 20 th Const- Commissioning Detector Data taking ruction data taking refurbish Rn calibration Feb. 1 st ～ 20 th . • Stable data taking from 2013 Nov. to 2019 Feb. (LT=1807.3 day) • We achieved the objectives of XMASS-1 XMASS and shut down on Feb. 20 th , 2019. 5
1898.4 calendar days DAQ r untime = 1807.3 days Good run = 1638.9 days (86.3 %)
ACHIEVEMENTS IN XMASS-I • Dark matter searches • Neutrino studies • Other exotic physics (Axion, …) • Solar axion, KK axion, • Neutrino observatory • Low background technology
DARK MATTER SEARCHES IN XMASS-I -- ANNUAL MODULATION • DAMA/LIBRA’s claim (https://doi.org/10.15407/jnpae2018.04.307 ) • The data of the new DAMA/LIBRA-phase2 confirm a peculiar annual modulation of the single-hit scintillation events in the (1 - 6) keV energy region satisfying all the many requirements of the DM annual modulation signature; … (1.04 + 1.13) ton*year, 13 cycles
• Annual modulation search with the XMASS (10.1103/PhysRevD.97.102006) • Target volume = 800 kg, Livetime = 800 days (1.82 ton*year, 2.2 cycle) Assuming WIMP DM, we excludes DAMA/LBRA allowed region at 3σ level by annual modulation.
In model independent analysis, we found no periodicity in data.
DARK MATTER SEARCHES IN XMASS-I -- ANALYSIS WITH EVENT RECONSTRUCTION 57 Co 122keV • Event reconstruction in XMASS: • Event energy and position can be reconstructed with numbers of P.E. in each PMTs. p i (n) : probability that the i -th PMT detects n PE • Strong self-shielding could lead small numbers of BG at the center region, r<20 cm.
RESULTS: ENERGY SPECTRUM IN THE FIDUCIAL VOLUME • 706 live days taken in Nov. 2013 – Mar. 2016 • Fiducial mass 97kg (R<20cm) • Main background in the WIMP search region 210 Pb in the copper g -rays from PMTs Neutrons, alpha-rays are negligible 13 10.1016/j.physletb.2018.10.070
RESULTS: ENERGY SPECTRUM IN THE FIDUCIAL VOLUME • 706 live days taken in Nov. 2013 – Mar. 2016 • Fiducial mass 97kg (R<20cm) • The energy spectrum at 2-15 keV ee is fitted with signal + background. 14 • Systematic uncertainties are taken into account as nuisance parameters in the fit. Detector surface conditions (gap, roughness) are dominant.
• 97kg x 706 days exposure • 90% CL upper limit on SI WIMP-nucleon cross section • s SI <2.2x10 -44 cm 2 @60 GeV/c 2 • First stringent constraint by a single-phase LXe detector. 15
DARK MATTER SEARCHES IN XMASS-I -- HIDDEN PHOTONS & AXION-LIKE PARTICLES DARK MATTER • Hidden photon (HP): gauge boson of hidden U(1) Both are the cold dark matter Axion-like particles (ALPs): pseudo-Nambu-Goldstone boson candidates. • Both bosons can be absorbed in the detector medium with emission of an electron. analogue to photoelectric effect 𝜏 𝑞𝑓 𝜕 = 𝑛 𝐼𝑄 𝑑 = 𝛽 ′ 2 𝜏 𝑏𝑐𝑡 𝑤 𝜏 𝑞𝑓 𝜕 = 𝑛 𝐵𝑀𝑄 𝑑 = 3𝑛 𝐵𝑀𝑄 𝜏 𝑏𝑐𝑡 𝑤 2 2 × 𝐵𝑓 𝛽 16𝜌𝛽𝑛 𝑓 16 2 x m ALP • Event rate ∝ (a’/a)/ m HP or g Ae
THE RESULTS • 800 live days of data (Nov. 2013 – Jul. 2016) • Fiducial volume was extended to R<30cm (327 kg of LXe) • Fitting energy range 30-180 keV • A peak search by fitting the energy spectrum with the signal + background model. • Scanning mass every 2.5 keV/c 2 in 40-120 keV/c 2 17 https://doi.org/10.1016/j.physletb.2018.10.050
No significant signal was observed. • Hidden photon DM • Axion-like particles DM a ’/ a < 6x10 -26 (90% CL) for 40-120 keV/c 2 g Ae < 4x10 -13 (90% CL) for 40-120 keV/c 2 Cover a region where indirect searches are weak Cover higher mass region than LUX and PandaX-II • The best constraint in 40-120 keV/c 2 for both cases. • For HP, no possibility for thermal production mechanism for the first time in the world in the 18 previous work in 2014. ( DOI: 10.1103/PhysRevLett.113.121301)
STUDIES ON NEUTRINO PROPERTIES WITH XMASS -- DOUBLE ELECTRON CAPTURE • Natural xenon contains 124 Xe (N.A.=0.095%) and 126 Xe (N.A.=0.089%) 2 - 4.2d 0 + 124 I which can undergo double electron capture. 53 124 Xe 54 124 Xe (g.s., 0 + ) + 2 e - 124 Te (g.s., 0 + ) + (2 n e ) + 2864keV Q ECEC =2864keV 0 + • 0 n mode Evidence of lepton number violation 124 Te 52 2 n mode New input for nuclear matrix element calculation • None of the modes are overserved yet. 23
124 Xe 2 n double electron capture from K-shell (2 n 2K) • • Total deposit energy of 63.6 keV by X-rays/Auger electrons n K-shell X-ray • Expected half-life is 10 20 -10 24 years. … Xe • It may be possible to find out the 2ν2K. • Main BG: 125 I • 125 I + e - 125 Te + ν + 185.77 keV, T 1/2 =59.4 day n K-shell X-ray • It is created by thermal neutron capture of 124 Xe outside the water shield. • It gives a peak at 67.5 keV ee . 24
Result (DOI: 10.1093/ptep/pty053) We divided the data into 4 by operation modes. In each operation modes, thermal neutron flux is measured by 2 n 2K independent measurement. 125 I 25 • No significant signal was observed.
• The most stringent limit to date 2 n 2K ( 124 Xe)>2.1x10 22 T 1/2 yrs 2 n 2K ( 126 Xe)>1.9x10 22 T 1/2 yrs The result ruled out some theoretical predictions. Excluded Note on theoretical predictions: 26 • g A = 1.26(lower) – 1(upper) • Probability of 2K-capture= 0.767
NEUTRINO OBSERVATORY, XMASS • XMASS has the sensitivity to detect neutrino burst from a supernova around 10 kpc via neutrino coherent scattering Supernova rnova model d=10 0 kpc d=196 96 pc Livermore 15 3.9x10 4 Nakazato (20M solar , Z=0.02, t rev =100ms) 3.5 0.9x10 4 n n A A Nakazato (30M solar , Z=0.02, t rev =300ms) 8.7 2.3x10 4 Nakazato (black hole) 21 5.5x10 4 K. Abe et al. (XMASS Collaboration), Astropart. Phys. 89 (2017) 51-56
• Especially for nearby-supernova case, • KL can measure pre- SN ν to distribute SN alert. • XMASS can measure 10 4 events • We established SN monitoring network in Kamioka. • Monitor SN alert provided by KL in 24 hours. Pre-supernova neutrinos
• The result: • We are not lucky enough to observe any SN ν in this 30 years. • But it is shown by XMASS that a large scale DM detector is potentially utilized as SN ν observatory.
• Other astrophysical object: • We searched for event bursts related to GW170817. Around GW170817 (Aug. 17 2017 12:41:04UTC) in [-400, +10,000] sec Simple data reduction: <~30 keV Full volume No OD trigger -- Inner det. trigger -- After all cuts Removing PMT after pulses Remove Cherenkov events Four evet regions <~30 keV 0.22 event/s 30-300 keV 0.56 event/s 300-3000 keV 0.99 event/s >~3000 keV <~30 keV 0.02 event/s Analysis Window 3,000 keV< 30-300 keV 300-3,000 keV Vary from 20 ms to 10 s to find bursts.
GW170817 <~30keVee BG rate estimated -400 -300 -200 -100 0 100 200 300 400 [sec] from pre-window 30-300keVee of GW170817 300-3000keVee >~3000keVee To be published soon! No bursts were found.
LOW BG TECHNOLOGY • Introduction: • The main backgrounds of the XMASS detector are • 210 Pb from cupper and • RI’s from the PMT. • We have lots of efforts. • Three topics in this talk: • New 3” round -shape PMTs • Particle ID by Xe scintillation property • Ultra low level α counter
LOW BG TECHNOLOGY -- PARTICLE ID BY XE SCINTILLATION LIGHT • Nuclear scattering from electron scattering • With neutron source, scintillation time profile are measured. https://doi.org/10.1088/1748-0221/13/12/P12032
• Acceptance of electron recoil events assuming • Log likelihood ratio 50% acceptance of 100 GeV WIMPs. With jitter Without jitter It is not easy to distinguish NR from ER at lower energy region.
• Electron event from gamma evet • Gamma ray interacts with electrons and looses the energy. • This reads the time profile difference between gamma and electron. 𝑜−1 − ln 𝑄 𝑗 𝑜 𝑄 = ෑ 𝐷𝑀 𝑗 βCL = 𝑄 × 𝑗! 𝑗=1 𝑗=0 214 Bi b -ray (30-200 keV ee ) 241 Am 60keV g -ray This method is applied to the 124 Xe 2ν2K analysis. S/N is improved by factor 5.
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